Hip dysplasia is a condition in which there is abnormal development of the coxofemoral joint (i.e., the hip joint), which includes a femoral head (i.e., a ball) and an acetabulum (i.e., a socket). It is estimated that up to 20% of all canines suffer from some degree of hip dysplasia. Hip dysplasia causes poor congruency between the surfaces of the femoral head and the acetabulum, which leads to increased movement between the femoral head and the acetabulum and increased friction as the animal moves the coxofemoral joint. Over time, the increased friction in the coxofemoral joint leads to pain and inflammation in the hip, which in turn leads to decreased activity, muscle atrophy, thinning of the articular cartilage, and irritation of the surrounding soft tissue.
Static stability of the coxofemoral joint is provided by the femoral head sitting partially in the acetabulum, the labrum of the acetabulum, which covers a dorsal portion of the femoral head, and a ligament that extends between the medial side of the femoral head and the acetabulum. Fibrous tissue in the coxofemoral joint also aids in providing static stability.
In a healthy coxofemoral joint, approximately 50% of the femoral head is covered by the acetabulum. In contrast, in an animal with hip dysplasia, the dorsal lip of the acetabulum does not adequately cover the femoral head such that significantly less than 50% of the femoral head may be covered by the acetabulum. In extreme cases, the femoral head may luxate (i.e., dislocate) dorsally over the rim of the acetabulum as the animal stands up or walks.
Additionally, in a healthy animal, the animal's muscles around the coxofemoral joint, such as the gluteal muscles, the iliopsoas, the gemelli, the quadratus femoris, and the internal and external obturator muscles, aid in keeping the femoral head firmly seated in the acetabulum. In contrast, in an unhealthy animal suffering from hip dysplasia, the chronic pain associated with hip dysplasia can inhibit muscular action and can lead to atrophy of the muscles that help seat the femoral head in the acetabulum.
Related art methods for treating hip dysplasia include medications/supplements, rehabilitation therapy, surgical correction, and/or braces. However, medications and supplements are costly and can cause negative side effects on the animal's liver and kidneys when used for an extended period of time. Related art surgeries are expensive, require a period of restricted activity to permit proper healing, and can result in serious complications, such as infections and, in the case of a total hip replacement, loosening of the hardware or subluxation of the prosthetic hip. Additionally, related art hip braces artificially restrict movement around the hip joint, which can cause further atrophy of the muscles that aid in seating the femoral head in the acetabulum.